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Discussion Starter · #1 ·
i just registered on this site and i cant find where to post a question,, < ~~~ this site is MESSED UP !!!,,,

my bike has a 110 90 18 on the rear,, how big can i go?? what size??? my bike is stock 78 cx500
 

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i just registered on this site and i cant find where to post a question,, < ~~~ this site is MESSED UP !!!,,,

my bike has a 110 90 18 on the rear,, how big can i go?? what size??? my bike is stock 78 cx500
A larger tire is going to make turn in slower, so what exactly are you trying to accomplish?
 

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you must of seen his reply because you replied to him and i am sorry if you think this site is messed up and i am pretty sure if you keep talking crap you wont be around long



thats just my 2 cents and thats all i am going to say
 

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you must of seen his reply because you replied to him and i am sorry if you think this site is messed up and i am pretty sure if you keep talking crap you wont be around long



thats just my 2 cents and thats all i am going to say
He's having problems with the forum UI, he wasn't giving me flack about my post.



I'm going to quote the PM he sent me as it appears to be intended for this thread.



Bad Ass 78 CX 500 said:
i know larger with run at lower rpm and raise my seat height a little,

my 110 90 18 wimpy, i want fatter with out rubbing the swing arm,

swig arm clearance and not raising the height of the bike are the two concerns,,

WHERE DO I GO TO POST,, HOW DO I RESPOND,, THIS SITE IS MESSED UP, it gives you font choices and freakin sizes but no direction on how to post, thanks for your help


So you're sort of on the right track with large tire diameter reducing RPMs and raising the bike, but what I said was that a wider rear tire will cause the bike to TURN IN slower.



As for how wide a tire you can fit inside the swing arm, measure the clearance on each side, pick the smaller of the two numbers and add double that amount to the section width of the tire you're currently running. Then find a tire that does not exceed this.



Of course tire measurements greatly depend on the width of the rim the tire is intended to be mounted on, and measurement tolerances vary between manufacturers (a 120/90-18 might actually be 122 in one case and 118 in another.)



The rear rim on the '78 is 2.15x18, which is quite narrow and will change the profile of a wider tire intended to fit a wider rim. This will make for unusual handling on it's own but will interact with the slower turn in I mentioned earlier.



This all goes back to my original question of "what are you trying to accomplish by using a wider tire?"



I'm running a 120/80-18, because that was the nearest size I could get a specific tire in. I've adjusted to the handling problems this creates because the net effect of the tire type was greatly beneficial for the type of riding I enjoy.



If you're just trying to put a fat tire on for looks then nothing I've said really matters anyway, except for the part about measuring swing arm clearance.
 

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The largest tyre you can effectively run will be a 130/90-16 (or MT90-16) as is, on a wheel assembly

A wider tyre will not necessarily make the bike turn in slower as speed of turn in has nothing to do with width, but is controlled by profile and diameter. 130/90-16 being predominantly a touring size it is liable to have a slower profile, but not necessarily so. The "peakier", or more triangular the profile the faster it will turn in, but it will wear in the centre faster as the vertical footprint will be less, and the "flatter" the profile is the slower it will be to initiate a turn, but the wear will be correspondingly lower also, so your choice should be made around these features.

However, consider this

a 120 profile tyre may well be effectively wider than a 130 profile from brand to brand. The 130 tyre is really intentioned to be at its correct width on a wider rim (a minimum of a 3" rim as opposed to the CX 2.75vrim width), so the profile will be incorrect on a CX rim and not all of it will be able to be used on the road. This could well lead to it having 8-10 mm of unusued rubber at its edges making it in effect a 110 (130-(10x2). A properly profiled 120 that can be scrubbed to its edges becomes in reality a wider tyre, and its increased diameter will alter the rake, trail, and caster enough to make a difference

A 120/90-18 Avon Roadrider for example measures 129mm on a 2.75 rim, wheras a 110/90-18 measures 116 on a 2.50 rim (so probably about 119 on a 2.75)

However an MT90-16 measures 137 on a 3.00 rim ( so probably about 135 on a 2.75). However since the edges of the profile are now not correct it will almost certainly be effectively no wider than the 120, and although it will steer faster it will lose out in terms of load carrying capability by 187lbs
 

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Discussion Starter · #10 ·
theres a lot more to tires than i thought, im sticking with my stock 18" rim, im leaning towards the 120 90 18











The largest tyre you can effectively run will be a 130/90-16 (or MT90-16) as is, on a wheel assembly

A wider tyre will not necessarily make the bike turn in slower as speed of turn in has nothing to do with width, but is controlled by profile and diameter. 130/90-16 being predominantly a touring size it is liable to have a slower profile, but not necessarily so. The "peakier", or more triangular the profile the faster it will turn in, but it will wear in the centre faster as the vertical footprint will be less, and the "flatter" the profile is the slower it will be to initiate a turn, but the wear will be correspondingly lower also, so your choice should be made around these features.

However, consider this

a 120 profile tyre may well be effectively wider than a 130 profile from brand to brand. The 130 tyre is really intentioned to be at its correct width on a wider rim (a minimum of a 3" rim as opposed to the CX 2.75vrim width), so the profile will be incorrect on a CX rim and not all of it will be able to be used on the road. This could well lead to it having 8-10 mm of unusued rubber at its edges making it in effect a 110 (130-(10x2). A properly profiled 120 that can be scrubbed to its edges becomes in reality a wider tyre, and its increased diameter will alter the rake, trail, and caster enough to make a difference

A 120/90-18 Avon Roadrider for example measures 129mm on a 2.75 rim, wheras a 110/90-18 measures 116 on a 2.50 rim (so probably about 119 on a 2.75)

However an MT90-16 measures 137 on a 3.00 rim ( so probably about 135 on a 2.75). However since the edges of the profile are now not correct it will almost certainly be effectively no wider than the 120, and although it will steer faster it will lose out in terms of load carrying capability by 187lbs
 

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Discussion Starter · #11 ·
you say a 130 will fit,, is that a 130 90 18? which will raise my bike by 18mm as compared to the 110 90 18

im running now, this is why im leaning towards the 120 90 18 which will only raise my bikes rear by 9mm,

and may better fit my stock 2.75" wide rim



The CX is not easy to put a wide tire on the rear. The 18" rear wheel can fit a 130 in a pinch but a 120 is standard which is what I run.

The 16" rear wheel (interchangable) is a wider Cruiser look and can fit a 140. Welcome to the board.

Cheers, 50gary
 

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Discussion Starter · #12 ·
i messed up my rim is 2.15" wide,, im still think the way to go is from my 110 90 18 to a 120 90 18



The largest tyre you can effectively run will be a 130/90-16 (or MT90-16) as is, on a wheel assembly

A wider tyre will not necessarily make the bike turn in slower as speed of turn in has nothing to do with width, but is controlled by profile and diameter. 130/90-16 being predominantly a touring size it is liable to have a slower profile, but not necessarily so. The "peakier", or more triangular the profile the faster it will turn in, but it will wear in the centre faster as the vertical footprint will be less, and the "flatter" the profile is the slower it will be to initiate a turn, but the wear will be correspondingly lower also, so your choice should be made around these features.

However, consider this

a 120 profile tyre may well be effectively wider than a 130 profile from brand to brand. The 130 tyre is really intentioned to be at its correct width on a wider rim (a minimum of a 3" rim as opposed to the CX 2.75vrim width), so the profile will be incorrect on a CX rim and not all of it will be able to be used on the road. This could well lead to it having 8-10 mm of unusued rubber at its edges making it in effect a 110 (130-(10x2). A properly profiled 120 that can be scrubbed to its edges becomes in reality a wider tyre, and its increased diameter will alter the rake, trail, and caster enough to make a difference

A 120/90-18 Avon Roadrider for example measures 129mm on a 2.75 rim, wheras a 110/90-18 measures 116 on a 2.50 rim (so probably about 119 on a 2.75)

However an MT90-16 measures 137 on a 3.00 rim ( so probably about 135 on a 2.75). However since the edges of the profile are now not correct it will almost certainly be effectively no wider than the 120, and although it will steer faster it will lose out in terms of load carrying capability by 187lbs
 

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Wow this guy must be having some bad luck. Just quotes. Maybe he should go to the bottom of the page where it says fast reply and type there and then hit the post button.
 
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