Author Topic: 18 vs. 19 inch Front Wheel (Read 15268 times)

stueveone · « **on:** December 25, 2011, 10:26:40 AM »

Hey guys,
Preparing for a wheel build over here consisting of Excel shouldered rims and ss spokes, and I am having a hell of a time trying to decide on wether or not to stick with the stock 19 inch front or step it down to the 18?

Here's the pros and cons as I see 'em;

18 inch rim
PROS: Better handling, wider range of tire choices, some prefer looks.
CONS: Would have to get different fender, speedo drive, and tire. Some prefer 19 inch looks.

What do you guys think? Is the handling and performance of an 18 inch front wheel that much better? Also, let's see some photos if you got em!

Thanks!
stueve

HondaMan · « **Reply #1 on:** December 25, 2011, 10:49:03 AM »

The 18 inch front will produce WORSE handling, not better. It shortens the already too-short trail on most of these SOHC4 bikes. The 750, for example, has just 3.75" of trail when new, and typically 3.6" trail after the springs have sacked (after 5 years of sitting on their forks), and the 500/550/350/400F are even worse.

What is advisable: either stick with the 19" front, and add air forks, or get longer forks by 1 or 2 inches, and add a rigid fork brace f you go to 18" rim.

Those who have ridden long time or raced these chasses will tell you the same.

TwoTired · « **Reply #2 on:** December 25, 2011, 10:55:55 AM »

Essentially, if you have to ask, then stick with the stock size that was engineered for the bike. IMO

I don't think a smaller front makes the SOHC4 a "better" handling bike. But, it will be "different".
Smaller may be better for low speed trips about the shopping mall. But, it will be far less stable on the Bonneville track.

If you are changing the engineering of a machine, know the purpose first. Otherwise, you are just making solutions to a problem you haven't identified.

What extreme use do you wish to participate in that the stock size is inadequate?

If it is just for looks while parked, then do whatever pleases you. Practicality doesn't matter with aesthetics.

Cheers,

stueveone · « **Reply #3 on:** December 25, 2011, 11:23:31 AM »

Hey, thanks for the quick reply guys! And on Xmas no less!
I've only read here, on the forum, that the 18inch wheel handled better. Which is kind of why I wanted to throw this post out there.
The impetus for my build has always been performance, with looks taking a close second

So if there are no real appreciable handling gains but rather noticeable losses, then looks like I'll be keepin' her stock!

Also, the CR750's had 18's in the front, right? Was the fork geometry different to account for this?

Cheers!
stueve

754 · « **Reply #4 on:** December 25, 2011, 11:54:59 AM »

Keep in mind the 100 bux worth of spokes that adds to the cost.. just saying.....

TwoTired · « **Reply #5 on:** December 25, 2011, 12:00:06 PM »

What aspect of "performance" or the performance envelope are you trying to change? Describe what would make it "better" for you. Or, what don't you like about the stock set up? (Other than it is stock).

faux fiddy · « **Reply #6 on:** December 25, 2011, 04:06:16 PM »

Quote from: TwoTired on December 25, 2011, 12:00:06 PM

What aspect of "performance" or the performance envelope are you trying to change? Describe what would make it "better" for you. Or, what don't you like about the stock set up? (Other than it is stock).

On the 450's cb has 18" and CL has 19" wheels. I think the frame and triple clamps are identical. Which configuration has any advntage?

TwoTired · « **Reply #7 on:** December 25, 2011, 05:08:55 PM »

Quote from: fiddy of industry on December 25, 2011, 04:06:16 PM

Quote from: TwoTired on December 25, 2011, 12:00:06 PM
What aspect of "performance" or the performance envelope are you trying to change? Describe what would make it "better" for you. Or, what don't you like about the stock set up? (Other than it is stock).

On the 450's cb has 18" and CL has 19" wheels. I think the frame and triple clamps are identical. Which configuration has any advntage?

CB was a street bike designator. CL was an off-road (before dual sport became vogue) or combined use designator and often had high mounted pipes for terrain clearance. Nice flat surfaces don't strictly need large wheels, as there are not many or at least smaller pits/holes to traverse. But, when driving over obstacles, a larger diameter wheel is more likely to traverse those obstacles and holes in terrain. It is beneficial to not have your front tire stop suddenly in a hole or at large bump while driving.

Larger wheels also reduce rotation speeds for any given distance. Larger wheels can last longer (get higher mileage) in use as there is more tire tread in circumference. Notice semis have very tall tires? In great part, that is for economy.

For the open road, a larger diameter tire can have less rolling resistance and/or create a larger contact patch for the tire to road, (given the same width tire as the one in smaller diameter).

Attention must be also be paid the the overall mass of the wheel/tire combination. Sometimes, larger wheels can be heavier, and angular momentum forces effect how the bike feels when turning.
If the smaller wheel also has a fatter tire on it to regain or increase contact patch size. The resulting mass may well be greater than the larger wheel/tire combo.

Conservation of Angular Momentum

If you are reversing lean angles fast and furious, a smaller/lighter front rotating mass can help do that, given the rest of the bike's geometry is set up for it. I think a lot of bikes with small front wheels also have geometry coordinated, as well as a steering damper to keep the bike stable at high speed.

When making a change, it is nice to know what the goals are beforehand or what the existing "performance" is. Otherwise, it's just a change for change sake, and there is no way of knowing whether "improvement" took place.

Cheers,

seanbarney41 · « **Reply #8 on:** December 25, 2011, 08:32:30 PM »

18" is going to increase your ability to turn sharper quicker or "turn in", but reduce your high speed stability (probably to the point where the bike is no longer safe without a steering dampener).a similar result can be achieved with longer than stock rear shocks

stueveone · « **Reply #9 on:** December 26, 2011, 02:50:08 PM »

Cool. Well thanks for the info guys. I had been doing some reading on the forum about members noticing a beneficial difference in handling, ie quicker steering etc. I was just curious if it was worth the fuss and if the CB750 frame geometry lent itself better to an 18 inch wheel (again, seeing it on those CR750's made me wonder). Also, seems like most sport bikes these days have the same size wheel front and back, so wasn't sure if there was any particular reason, besides tire availability.

Cheers!
stueve

Tim2005 · « **Reply #10 on:** December 26, 2011, 02:52:44 PM »

I have found that an 18" front rim is an excellent improvement, to both the 550 and 750, improving cornering turn-in greatly. It does not make the bike unstable enough to need a steering damper - my 550 with an 18" rim is still more stable than my 400f which has an 18" rim stock, and nobody thinks of the 400 as an unstable bike. I think it comes down to how the geometry is so relaxed on these bikes. I have also found that the 18" is less prone to causing those gentle side-to-side bar movements through long high-speed sweepers that a 19" rim can exhibit.

Retro Rocket · « **Reply #11 on:** December 26, 2011, 04:05:31 PM »

Quote from: Tim2005 on December 26, 2011, 02:52:44 PM

I have found that an 18" front rim is an excellent improvement, to both the 550 and 750, improving cornering turn-in greatly. It does not make the bike unstable enough to need a steering damper - my 550 with an 18" rim is still more stable than my 400f which has an 18" rim stock, and nobody thinks of the 400 as an unstable bike. I think it comes down to how the geometry is so relaxed on these bikes. I have also found that the 18" is less prone to causing those gentle side-to-side bar movements through long high-speed sweepers that a 19" rim can exhibit.

+1
18 inch front conversion is very popular with guys that race these bikes, i have piles of pics of 750's and 550's with 18 inch fronts and there's quite a few of them on this site. If you are doing the conversion on a 750, use the F model clamps, they have a smaller 50mm offset {60mm on the K models} that will help keep the trail closer to stock....I am using 18 inch rims front and back on my K2 and 17 inch rims front and back on my F, i am also having custom made triple clamps made to keep the trail closer to stock. A steering damper is a good addition to our bikes even with the 19 inch front wheel as these bikes do have a small trail number stock and can be quite nervous on bumpy roads or at high speed.... The availability of good rubber is a good reason to consider using an 18 inch front wheel.
You can use a 400F speedo drive....
Here's some 18's...

HondaMan · « **Reply #12 on:** December 26, 2011, 10:40:18 PM »

Quote from: stueveone on December 25, 2011, 11:23:31 AM

Hey, thanks for the quick reply guys! And on Xmas no less!
I've only read here, on the forum, that the 18inch wheel handled better. Which is kind of why I wanted to throw this post out there.
The impetus for my build has always been performance, with looks taking a close second
So if there are no real appreciable handling gains but rather noticeable losses, then looks like I'll be keepin' her stock!

Also, the CR750's had 18's in the front, right? Was the fork geometry different to account for this?

Cheers!
stueve

Yes. The front forks were 1.8" longer (and had 4.1" travel) from the Yoshimura roadracing kit, and the front rim was thicker and wider, sporting a 4.00 size tire. The rear had a special 4.25 size tire to match, and a steering damper and fork brace, with a raised front fender to clear the tire and brace, can be seen in the famous "kit pictures" of the 1970s. The front dampers were set for more rebound damping by about 25% or so, and the rear shocks had larger pistons inside than the production versions, with 10mm more travel. Final trail was a shade over 4".

Retro Rocket · « **Reply #13 on:** December 26, 2011, 11:29:24 PM »

Didn't Honda change fork length on the 750's at some point also. ?

Stueveone, there's another way you can mod the front relatively easy to take an 18 inch front, if you want trail to remain the same, i am using GSXR1100 forks on my bike and they were about an inch shorter than the Honda forks, i had 2 inch {50mm} screw in extensions made to lengthen them so i had some room to move when setting up the suspension, Worked very well.....

Raul CB750K1 · « **Reply #14 on:** December 26, 2011, 11:57:18 PM »

In Spain, DMV allows the use of different tires as long as the new one has a circumference that doesn't exceed plus or minus 3% from the original.

In my modern Suzuki GZ250, I wanted a fatter front tire just for looks. Being a 250 cc, I was not much concerned about performance, and being a cruiser, not about cornering either.

Well, the bike has a 130/90-15 rear, and a 110/90-16 front. What I did was to lace a rear rim to a front hub, and use a rear tire in the front. I made it 2 cm wider, and the circumference falls into the +-3% allowed by the DMV.

First thing I noticed was a different sensation when cornering. I was not able to describe it, but the bike felt different. Not better or worst, just different.

If the circumference is the same, if you use a smaller rim, you need to add more rubber. As long as the circumference is the same, the gyroscopic effect must be similar at the same speed, not counting the difference in mass.

After some minutes, I got used to the new feeling on cornering. Some people say it is due to the fact that I'm using exactly the same tire both front and rear, thus, when cornering, both tires lean the same.

My point is that you can go from a 3.25-19 to a 4-18, you get a wider front tire -I like it-, keep the original circumference -more or less-, and use the same tire than the rear.

In any case, I did it because I wanted to try. The worst that can happen is that you spend some money, improve your lacing -and balancing- abilities, and waste some time installing and removing wheels. You can always get back to your original tire if you don't like the result. I say: go for it!

voxonda · « **Reply #15 on:** December 27, 2011, 12:05:16 AM »

Just want to react. I ride the 750's of mine for the last 4 decades and always changed over to 18" front. Never had any reason to go back to 19". But................... Like Hondaman says, you have to do some more to make it work properly. In a otherwise standard setup, standard, bike it gives very little to no advantage other than, very, low speed handling, and worse handling at speed, even up to dangerous levels.
First of all I use frontforks from the (900)DOHC series and their triples so to extend the trail. These forks are also longer and have better mounting possibilities for other, much, better brakes. Also have a extended swingarm which gives much more stability. And I have no need for using a steering damper.
A few years back build a bike for a customer who wanted 18" front. I used parts from the 400F. Made sure all the pivot area's wprked fine. Headstock and swingarm bearings, good tires and heavier front springs with altered damping rods for heavier damping. He still has and rides to this day.

Happy holidays, Rob

Terry in Australia · « **Reply #16 on:** December 27, 2011, 02:42:24 AM »

In racing circles, the 18" front wheel conversion has been common practise with big Jap bikes of the era for as long as I can remember. My Gold K2 with 41mm front forks and 18" wheel, which was built by a well known Aussie race bike engineer is the best handling CB750 I've ever ridden, and coincidentally, the only CB750 I've ridden with an 18" front wheel.

The steering is slightly quicker than with the 19" hoop, but with the wider front and rear tire, it felt like I could lean it over further, and I could certainly get around tight corners with less effort than on my other CB750's. I didn't notice any less stability at all, and I regularly saw 100+ MPH speeds, on some pretty crappy secondary roads.

I'd have no hesitation recommending the conversion, if only for the opportunity to access a better range of tire choices. Cheers, Terry.

Retro Rocket · « **Reply #17 on:** December 27, 2011, 04:09:27 AM »

I forgot about yours Terry, i love that bike....

Ricky_Racer · « **Reply #18 on:** December 27, 2011, 10:54:37 AM »

What find of 41mm forks did you use, Terry? And are they the same as on your lime/yellow bike? Thanks! RR

Terry in Australia · « **Reply #19 on:** December 27, 2011, 03:36:47 PM »

Quote from: Ricky_Racer on December 27, 2011, 10:54:37 AM

What find of 41mm forks did you use, Terry? And are they the same as on your lime/yellow bike? Thanks! RR

G'Day Mate, they're 1987(?) Yamaha FZR1000 forks and brakes. The PO initially used the Yamaha triples but the geometry was too severe and it was scary in tight corners, so he machined up some new triples with the OEM Honda offset. I've got some more 41mm forks here, and I'm just waiting for a member here to get his new CNC mill going so I can order another set of triples, and I'll do the same conversion on another CB750 I'm building. Cheers, Terry.

HondaMan · « **Reply #20 on:** December 27, 2011, 09:43:13 PM »

Quote from: Terry in Australia on December 27, 2011, 03:36:47 PM

Quote from: Ricky_Racer on December 27, 2011, 10:54:37 AM
What find of 41mm forks did you use, Terry? And are they the same as on your lime/yellow bike? Thanks! RR

G'Day Mate, they're 1987(?) Yamaha FZR1000 forks and brakes. The PO initially used the Yamaha triples but the geometry was too severe and it was scary in tight corners, so he machined up some new triples with the OEM Honda offset. I've got some more 41mm forks here, and I'm just waiting for a member here to get his new CNC mill going so I can order another set of triples, and I'll do the same conversion on another CB750 I'm building. Cheers, Terry.

Didn't those Yami triples have rake in them, beyond the frame? I seem to remember something like that...

Terry in Australia · « **Reply #21 on:** December 28, 2011, 12:00:10 AM »

Quote from: HondaMan on December 27, 2011, 09:43:13 PM

Quote from: Terry in Australia on December 27, 2011, 03:36:47 PM
Quote from: Ricky_Racer on December 27, 2011, 10:54:37 AM
What find of 41mm forks did you use, Terry? And are they the same as on your lime/yellow bike? Thanks! RR

G'Day Mate, they're 1987(?) Yamaha FZR1000 forks and brakes. The PO initially used the Yamaha triples but the geometry was too severe and it was scary in tight corners, so he machined up some new triples with the OEM Honda offset. I've got some more 41mm forks here, and I'm just waiting for a member here to get his new CNC mill going so I can order another set of triples, and I'll do the same conversion on another CB750 I'm building. Cheers, Terry.

Didn't those Yami triples have rake in them, beyond the frame? I seem to remember something like that...

G'Day Mark, the stock Yamaha triples (that I've still got in my garage) have no offset at all. The problem with them apparently was that they'd "Tuck under" in tight corners. Ken Piper (the engineer who originally built that bike) fixed the problem by machining up a set of triples to suit the 41mm forks with the CB750's offset. Cheers, Terry.

Ricky_Racer · « **Reply #22 on:** December 28, 2011, 08:33:43 AM »

Quote from: Terry in Australia on December 27, 2011, 03:36:47 PM

Quote from: Ricky_Racer on December 27, 2011, 10:54:37 AM
What find of 41mm forks did you use, Terry? And are they the same as on your lime/yellow bike? Thanks! RR

G'Day Mate, they're 1987(?) Yamaha FZR1000 forks and brakes. The PO initially used the Yamaha triples but the geometry was too severe and it was scary in tight corners, so he machined up some new triples with the OEM Honda offset. I've got some more 41mm forks here, and I'm just waiting for a member here to get his new CNC mill going so I can order another set of triples, and I'll do the same conversion on another CB750 I'm building. Cheers, Terry.

Thanks, Terry. I'm just looking around at possible modern dual-disk forks to use to (temporarily) replace the 41.3 tubes on my Rickman-Honda. Yours look like the one previously listed on Motocicli Veloci.

BTW, what did you use for the front hub? It seems that the Motocicli Veloci site no longer lists the hub and forks; it'd be nice to replicate the Rickman front hub for dual disks, but I'm afraid the costs would be prohibitive.

Thanks in advance. RR

Lostboy Steve · « **Reply #23 on:** December 28, 2011, 08:37:30 AM »

Wheel Woes. I swear you could spend more time deciding on a wheel / tire combo than anything else on these bikes. There are a million ideas and options. Good luck.

Ricky_Racer · « **Reply #24 on:** December 28, 2011, 08:43:19 AM »

Terry, I just found the forks in question at discovolantemoto.co.uk Described as "41 mm showa Forks (light and strong will not flex under braking)" At £1530.43, serious $$$! RR

Terry in Australia · « **Reply #25 on:** December 28, 2011, 02:16:04 PM »

Geez, you could buy a complete FZR1000 for that much money mate! Of course, if you had a nice FZR1000 you'd probably just ride it, they're a great bike. But I digress, the front hub is a standard CB750 hub with alloy adapter plates for the FZR1000 discs bolted on. Cheers, Terry.

Ricky_Racer · « **Reply #26 on:** December 28, 2011, 02:35:15 PM »

Got it, Terry. Thanks, Mate! So do you think the forks in the pic look like yours? They're the closest I've found so far.... RR

Terry in Australia · « **Reply #27 on:** December 28, 2011, 03:20:22 PM »

Yep, they're very close, I think Showa made them for a few different bikes. Just to add to your confusion, I almost bought a set of these 41mm Ceriani replicas recently, they're set up for Harleys so the tubes might be on the longish side, but they do look nice, and would suit a 70's era racer? Cheers, Terry.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=220871841062&ssPageName=ADME:X:RTQ:AU:1123

Ricky_Racer · « **Reply #28 on:** December 28, 2011, 05:18:47 PM »

Very cool, Terry. Pretty forks and a great price!

BTW, in your opinion, are 35mm Ceriani Roadrace forks strong enough for a 500 pound CB750? I haven't seen heavy replacement springs for these forks. RR

Terry in Australia · « **Reply #29 on:** December 28, 2011, 05:31:35 PM »

Well I'm sure that the purists and the techo-nerds here will jump all over me, but I don't reckon that the 35mm forks (any brand) were rigid enough mate. Don't get me wrong, they're adequate, just not great.

I know the Ceriani's are popular, but I don't really know why. I've got a pair here that I pulled apart to find out why they're so good, and they are totally unremarkable. I guess that they made a name for themselves back in the day when most Japanese forks were just two pieces of tube and a spring, but even the stock CB750 forks would be as good as Ceriani's of the era, I reckon.

Most modern bikes are running 41, 43, 45 mm forks or larger, and most modern bikes handle really well. It might be a coincidence, but I doubt it. Cheers, Terry.

camelman · « **Reply #30 on:** December 28, 2011, 09:28:18 PM »

Quote from: Terry in Australia on December 28, 2011, 05:31:35 PM

Well I'm sure that the purists and the techo-nerds here will jump all over me, but I don't reckon that the 35mm forks (any brand) were rigid enough mate. Don't get me wrong, they're adequate, just not great.

I know the Ceriani's are popular, but I don't really know why. I've got a pair here that I pulled apart to find out why they're so good, and they are totally unremarkable. I guess that they made a name for themselves back in the day when most Japanese forks were just two pieces of tube and a spring, but even the stock CB750 forks would be as good as Ceriani's of the era, I reckon.

Most modern bikes are running 41, 43, 45 mm forks or larger, and most modern bikes handle really well. It might be a coincidence, but I doubt it. Cheers, Terry.

Don't forget your trees. The forks are only as good as the parts that hold them.

Camelman

754 · « **Reply #31 on:** December 28, 2011, 10:00:15 PM »

You missed the part about Cerianis being a lot lighter... not to mention they are a lot easier to look at than a 70s Japan fork

754 · « **Reply #32 on:** December 28, 2011, 10:07:10 PM »

RR if the Cerianis can hold the Sorcerer in line up to 199mph, and keep a lot of double engine Harleys on the track, and all the XR750s on the oval, I doubt you will have trouble with them. They are made of pretty tough material, you would be scared if I told you how thin the lower legs are.. I bet if you turned a stock Hondas ones to that thickness, you could snap the lower leg with a well aimed kick..not kidding about that..

MCRider · « **Reply #33 on:** December 29, 2011, 09:54:55 AM »

Back to the original question...

I have an 18 on my project with the orignal fork and trees. So we'll get to see by my seat of the pants.

I chose this as an uninformed persons gut reaction that the 18 would handle better. I see that I simply was not considering all that may be affected by the change.

It is a considerably lighter combo, with a 110/80 tire, and aluminum Excel rim, than the 19" with a 110/90-19 i had been running. Man what an anvil that was! So one may think that will net out to the good.

I realize I shouldn't have had the 110, a 100/90 would have been better.

I did think ahead to buy new tubes from Franks that are 2" over stock. So i can restore or even increase the ride height and its change to trail. So here's hoping I'll find a combo I like. I have a beefy fork brace, and a tweak bar if necessary.

Gotta get it running first.

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Author Topic: 18 vs. 19 inch Front Wheel (Read 15268 times)