Topic: Skinnier tire up front for handling? CB550

[JZEROE]

Getting new tires next week--either Avon or Dunlop, because I want me some sticky. The manual--and info found on this forum--advises a 4.00x18 rear and a 3.25x19 front. I've had luck in the past squeezing a bit of extra agility out of a bike by narrowing the front tire. Anyone here have a similar experience? How narrow have you gone? I live up here in Northern Cali, where there are a lot of amazing, windy roads, and I do like to scrape those pegs...

[JZEROE]

Drat.

So I'm new to the forum, and didn't know you all were tired, as it were, of the rubber question. Please feel free to ignore my question; I'll just cruise the archives.

[goon 1492]

I'm sure as long as you stay as close to the spec size as possible you would be ok, too much change in size compared to rim fitment thought will change the geometry of the tire too much and could cause a unwanted flat spot or less surface to grip to when peg grinding, I'm no pro at tires so hopefully some one else chimes in with good info for ya.

[ohiocaferacer]

I've found with road racing the vintage bikes....that the closer the size of tires are to the front and rear...the bike handles alot better.

Example......running a 110/80 rear.....and running a 110/80 up front. The radius of the tire profile will be the same and the bike tracks straight in the corners as you roll over on the sides. On my 200gp bike......I run 90/90 x 18....front and rear.

Alot of the AHRMA guys are doing the same thing.

Just my 2cents

[scondon]

I'm sure as long as you stay as close to the spec size as possible you would be ok, too much change in size compared to rim fitment thought will change the geometry of the tire too much and could cause a unwanted flat spot or less surface to grip to when peg grinding, I'm no pro at tires so hopefully some one else chimes in with good info for ya.

   Having read earlier posts on the subject I found this point to be true, at least in my case. I switched from the 120/90/18(R),100/90/19(F) on my 750 to what the tire manufacturer recommended for my rim widths (2.15 and 2.15). Ended up with 4.00 rear and 90/90 front. The profiles are not "pinched" and the bike dips into corners a lot faster. The front diameter is a full inch shorter than the rear and I might try the 3.25 next time as it is only .2" shorter than the 4.00 rear. Avon Roadrider tires

I've found with road racing the vintage bikes....that the closer the size of tires are to the front and rear...the bike handles alot better.

Example......running a 110/80 rear.....and running a 110/80 up front. The radius of the tire profile will be the same and the bike tracks straight in the corners as you roll over on the sides. On my 200gp bike......I run 90/90 x 18....front and rear.

Alot of the AHRMA guys are doing the same thing.

Just my 2cents

   What brand of tires are you racing with? I've been looking for good, sticky stuff to fit the 19/18 rims on my 750 but can only find racing tires in smaller rim sizes.

[shoemanII]

i run the manufacturer's recommended tire sizes, 'cause i think honda picked them as a good compromise for their target audience.  just a guess tho.

if easier turn-in is your goal, try raising the forks in the triples.  i tried 5mm increments over the same route, and found 10mm to be just fine for my ride and riding style.  no real change at 5mm, better at 10mm and a tad twitchy at very slow speeds when set at 15mm.  the old boat now actually transitions pretty well if the road isn't all lumped up, and still has very good stability at all speeds. 

i personally wouldn't loose contact patch for ease of turn-in. 

good luck in your suspension tuning research, it's actually part of the overall experience i like.  a bit of advice is to make just one change at a time and test/feel the result.  tire pressure, fork oil, fork spring rates and preload, shock setting, front end geometry all enter into your quest.  have at it!   
bobp

       

[Tower]

Finally, someone asking th right questions!

Most tyre qustions are really concerned with looks and not with performance.

For performance (in order of importance):

• Match tyre compound to road surface conditions (wet/dry, rough/smooth, hot/cold, sticky/slick)
• Inflate tires to maximum pressure per tire spec
• Match tyre construction front to rear - don't put rear tyres on front or vise-versa, match void ratios to lug construction
• Avoid front tyres with centre groove lugs or with broad centre lug and high void ratios
• Select bias ply
• Match tyre width to rim width (reduce pinch angle - use lower range of tyre width spec for a particular rim - thinner is better)
• Use as close to 1:1 (100%) aspect ratio tyres as available (or higher speed rated construction if lower ratios)
• Match tyre height front to rear  e.g. 90/90-19 Front matches 110/80-18 Rear - use the Honda suggested Front tyre as the baseline height - deviation from this height will effect speedo readings as well
• Avoid rear tyres without edge stability features (such as sipes) and with low void ratio
  

[JZEROE]

Wow, Tower, that's very helpful. Now you get to see what an idiot I really am.

I don't really think I can go into the tire shop and speak intelligently about all the points you mention. I can stick with bias and pick my compound, no prob. I can inflate the tires to max spec, OK. I can use a front tire on the front, and a rear tire on the rear, and I can avoid grooves and big lugs in the center.

But the rest of your advice is a little greek to me. Some examples:

-->"match void ratios to lug construction."
I have no idea how I would go about measuring void ratios, or how I would match them to lug construction. I don't even know how I would quantify lug construction.

-->"Match tyre width to rim width (reduce pinch angle - use lower range of tyre width spec for a particular rim - thinner is better)"
So from this I get that I should stick with my stock rim width (3.25 on a '75 550, right?), but also that I should go as skinny as possible. So does that mean I should look for an 82.55/100 19 tire? Do they even make something like that? I see that Avon makes a Roadrider (looks like some pretty sweet rubber) with a designation "3.25B - 19," but I don't know what the aspect ratio on that is. I actually don't get that designation at all... Here's the link, maybe you can explain it (8th down from the top):
http://www.americanmototire.com/catalog/index.php?cPath=33_61_75

Sorry to be dumb, and thanks in advance for your help.

[Tower]

JZEROE, your questions are very good. I'm glad you asked them. Unless you're a tyre expert this info is rather Greek.

"match void ratios to lug contruction"
This item refers to the sturdiness (not squirmy)of the tread pattern.  The manufacturer always provides this data.  Ask the salesperson for this info and ask how the tyre you're interested in compares to another tyre with a different tread pattern.  What you are looking for is a low void ratio, i.e lots of rubber on the road, but not so low that it effects wet weather handling or makes the lug squirmy.  Again ask the salesperson to compare tread patterns using the void ratio.

"match rim width to tyre width"
Somewhere on this forum I posted some charts that show pinch angles plus an explanation of how its calculated.  (essentially, its the amount the tread overhangs the rim - the less the better) An angle over 16o is unstable in the corners and an angle over 20o might even be considered dangerous.
Your rim is probably 1.85" and 3.25-19 would be a great replacement tyre for that rim.  For the CB550, Honda recommends 3.15-19 or 3.25-19 (4 PR) ribbed tyres running at 26 - 29 PSI.  Also, that Avon tyre in your link has an aspect ratio is 97% giving you a wheel height of 25.3" and a pinch angle of 12.5o, which is very good for cornering stability.  A 90/90-19 tyre is not too bad at 90% aspect ratio, 25.4" wheel height but has a little poorer 14.9o pinch (its a little more wobbly around corners).

Sorry for the long delay in responding - got sidetracked by sexy exhaust pipes.

[JZEROE]

Wow. This is really interesting. Now if only you could educate my tire salesman... 

He can barely spell T-I-R-E... he uses a Y! Just kidding, but he is a genuine moron.

[Tower]

Us Canucks write in English.  You Yanks write in American 

[hapsh]

It seems that a lot of people tend to cram wider tires on these old bikes just for the look.  Sure, when you put your 75 CB550 with a 3.50x18 rear tire next to a 2005 CBR with a 190 rear tire it looks a bit skinny.  But that is all part of the vintage look.  I resisted the temptation to push the size limit on my 550 and went with Kenda Challenger 100/90x18 front and 110/90x18 rear and am VERY happy.  Handling is very tight and the traction is amazing.  Kenda Challengers are super sticky and soft, very comparable to Bridgestone Battlax BT014's.  I would have gone with a 90/90 front but the narrowest rear they had was a 110/90 and I wanted the front and rear to be as close as possible in width especially since I have 18" rims front and rear.

[andmoon]

The textbooks on riding say to get on the throttle thru a turn at a rate where the extra width of the rear tire (in comparison to the front) gets used up in accelerating the bike.

W/ tires of equal contact patch front and rear, is it correct to just maintain speed thru a turn? 

What you vintage racers say?

Don


ps.  I am new here, bringing me a 74 550Four home next week so that I can get my thrills at lower speeds.  ZRX1200 be my 'daily' bike.

[andy750]

This thread should be in the FAQ! Or Tower should write it up for "Towers thoughts" - great info here.

Mods?

cheers
Andy
 

[333]

Certainly refreshing to hear "How small can I go" versus "How big can I go".  You should get an award.

[upperlake04]

Us Canucks write in English.  You Yanks write in American 

 Excellent write-up Tower, but are you sure tyre is the favoured spelling in Canada? 

[magnus72]

why dont you guys stick to stock? Its confusing the #$%* out of me cause I need new tires.

I want some Dunlop K491 Elite 2s for my ride. What do I get thats closest to stock? I'm shopping on www.americanmototire.com

[JZEROE]

I stuck with stock, got a pair of Avon Roadriders as described earlier in this thread. I love them. They warm up quickly, grip like a flypaper/pumice mix, and don't track on grooved pavement. I have a feeling, though, that I'm not gonna get a lot of life out of them; nothing this sticky can last long.

[Tower]

Dunlop K491 Elite II on CB750 closest to Honda recommended, would be MM90-19 Front and 120/90B18 Rear.  Lower your rear shocks by 0.4" - 0.5" to return to stock aspect.  If you don't like raised white lettering, use the F24 100/90-19 tubed Front tyre instead.

[turboguzzi]

jumping a bit late into this but...

try see if you can get hold of Conti's TKV 11 front and TKV 12 rear. They are not a track compound like the KR124 / KR164 I run on my racer but some people do race with them and they are pretty cheap too.

TG

[lordmoonpie]

Us Canucks write in English.  You Yanks write in American 

 Excellent write-up Tower, but are you sure tyre is the favoured spelling in Canada? 

Oh yes it is - those nice Canadian Chaps like Tower use the Queen's english most appropriately....and so they should, we ENGLISH invented the darn tyres in the first place so get with the spelling you North American types....

Hey - haven't we been here on another thread in a galaxy a long time ago and really quite nearby? 

[upperlake04]

  Please correct me if I'm wrong M'Lord, but didn't a Scotsman invent the tyre?   

[TwoTired]

I thought they called them "pneus" in Canada.

[Gordon]

I thought they called them "pneus" in Canada.

Eh?

[scunny]

http://www.pneusmetro.com/