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LifesHarlequin
13th August 2008, 19:54
Which wheel and tire combination offers the best handling? From the basics of what I can find, the larger the wheels, the better cruising is, but if going for handling and road carving, I've seen a lot of mix between 17" and 18" wheels.

Has anyone done any testing or have any experience of which would be best for which application on a Sportster?

LifesHarlequin
13th August 2008, 21:28
Seems like all the Buells run with 120/70/17 front and 180/55/17 rear tires. Anyone installed a set of buell wheels on their Sportster and noticed a difference in flickability?

toe
13th August 2008, 23:54
The wider tires are better for cornering power.

Narrow tires make your bike feel more nimble

Albie1200
14th August 2008, 00:09
I was once told a taller wheel will resist leaning to the side due to gyroscopic effects. If it is true a bike with 17" wheels will enter a turn easier than a bike with 21" (front). Of course this is hearsay and I never claimed to be a physics major, so there is a good chance I am wrong.

stealthammer
14th August 2008, 00:36
The stickiest tires are usually only available in 17" (front/rear) and a few 18" (rear) these days. There is nothing really sticky is made in 21", only a few in 19". If you are going the really carve 17" is the way to go, but a 19" front and 18" rear is a distant second best choice. If you want the best handling you have to start at the tire, not the wheel size.

88inchsporty
14th August 2008, 20:21
I run radials. 120/60-17 front, and a 150/70-17 rear. Flickability is outstanding,as are all aspects of ride and handling. Responds quicker to rider inputs than my Buell X-1.

Moved On / My Own Choice
14th August 2008, 20:24
I think generalizations can be dangerous - you have to consider not only tire size, but construction/profile - radial vs. bia-ply for instance...

LifesHarlequin
15th August 2008, 20:13
I'm looking at getting a set of custom 40 spoke wheels (17x3.5 front and 17x5.5 rear) covered in Pirelli Diablo Strada tires (120/70 and 180/55),which is the same as the Buell. Can anyone see any problems with ride height or angle change? I know the height will be lower, and the wheel base slightly shorter, but with the angle being tilted downward toward the front, would this increase or decrease handling?

I know on cars, with the front in still in a dive, the car will handle lousy through a corner as the weight balance will be mostly on the front tires, which will cause understeer.. does this hold true for a motorcycle?

If so, how would I correct this? Lower the rear end via shock setup?

Brian73
15th August 2008, 20:22
The wider tires are better for cornering power.

Narrow tires make your bike feel more nimble


Narrower tires make your bike more nimble. For best cornering capability, in theory, you want your tires to only be as wide as they need to be to get the power to the ground without slipping. 250 cc 2-stroke bikes out-corner liter bikes on a road course while running only 150mm rear tires.

And, like Kev M said, width is only part of the equation.

LifesHarlequin
15th August 2008, 20:52
The Diablo Strada's are radial tires, and the 180 seems about the right size.. I'm more worried about the change in bike profile and how it will affect handling.

stealthammer
15th August 2008, 21:28
LifesHarlequin, you'll have to measure your existing wheel's OD to be sure about how much effect the 17s will have, but I'm betting that bringing the front end down a little will improve steering response.

LifesHarlequin
18th August 2008, 16:19
As ground clearance has a good bit to do with lean-angle, I was curious as to what was available in 18" wheels. Unfortunately there are no 180/55's available in a nice sticky Pirelli or Avon, so I went with 160/60's. I just need something that will help put down the planned 100rwhp from the proposed engine mods (listed in signature). But I'm wondering how much the flickability will change when going to 18's over the 17's. As for the tire question, the Diablo Strada is the tire of choice as I plan on this bike being a daily rider, and need the all weather tire.

After doing some calculations with RB Racing Pro Rake and Trail Calculator, this is what I came up with:

http://www.rbracing-rsr.com/advchoppercalc.html

Stock
29.6 Fork Angle in degrees
29.6 Steering Neck Angle in degrees
4.57 Trail in inches
60.0 Wheelbase in inches
52.3 Rear axle centerline to centerline top of fork tubes, inches
60.0 Rear axle centerline to front axle centerline, inches
39.1 Top of fork tube centerline to ground, inches

17" w/ 120/70 & 180/55 & Forks pulled 1" up through trees
28.8 Fork Angle in degrees
28.8 Steering Neck Angle in degrees
3.68 Trail in inches
59.5 Wheelbase in inches
51.9 Rear axle centerline to centerline top of fork tubes, inches
59.5 Rear axle centerline to front axle centerline, inches
37.2 Top of fork tube centerline to ground, inches

18" w/ 120/70 & 160/60 & Forks pulled 1" up through trees
28.8 Fork Angle in degrees
28.8 Steering Neck Angle in degrees
3.96 Trail in inches
59.5 Wheelbase in inches
51.9 Rear axle centerline to centerline top of fork tubes, inches
59.5 Rear axle centerline to front axle centerline, inches
37.2 Top of fork tube centerline to ground, inches

The rake and trail are definately shorter with the 17" and 18", as is the Wheelbase. These should add to the flickability and handling of the bike, but as to how much, I don't know.

A friend of the family used to be an editor for a motorcycle magazine, and he's been kind enough to forward the proposed specs to a field engineer that worked with his magazine for years. I'll let you guys know what he says.

LifesHarlequin
18th August 2008, 16:53
Just felt like getting my idea out on paper, so made a quick sketch of the bike:

http://xlforum.net/photopost/data/500/ColorBikeSketchMini.jpg

LifesHarlequin
19th August 2008, 05:31
There is not a definitive answer from the field engineer. In his opinion, the wheel mod might work, and it might not. The bike will be custom, and so its up to me to simply try different setups and see how they work out as my pockets empty.

Basically, they told me to check out Buell's if I want a true performance bike, as this is what the wheel mod is based off.

Unfortunately, the insurance for the Buell would simply void the original idea of saving money on the vehicular front. This brings up a very valid and mind refreshing point that the whole idea of the Sportster was to save money, and turning it into a cafe' racer, which will still only handle "almost" as good, but never as good as a Buell, makes the idea of spending $7,000 on modifications for the bike, rather contrary to the purpose of buying the Sportster in the first place.

Therefore, I will ride the bike bone stock with small upgrades, such as sissybar, quarterpanel, and reach solo seat, which was the idea for the first year anyhow, and then once my insurance rates take a more favorable turn, I'll pick up an XB12XT Ulysees, which is the bike I truly want anyhow, and would buy if only insurance would let up.

LifesHarlequin
20th August 2008, 16:24
Unless you re-raise the front end of the bike with longer forks or the like, changing to wheels which allow for Sportbike tires just to get lean angle and handling increase is actually counter-productive. The ground clearance you lose effectively reduces your lean angle as the part which would hard contact at 32 deg will only contact at a closer angle.

IMHO, unless you want to replace your forks, leave the front wheel alone and if you need more rubber in the rear, get a set of Dunlop K591's for grip and higher speed rating. Outside of that, you'll be spending way too much money just to get a little more handling, and even after all this you still have the weight of the bike to deal with.

88inchsporty
21st August 2008, 20:14
Unless you re-raise the front end of the bike with longer forks or the like, changing to wheels which allow for Sportbike tires just to get lean angle and handling increase is actually counter-productive. The ground clearance you lose effectively reduces your lean angle as the part which would hard contact at 32 deg will only contact at a closer angle.

IMHO, unless you want to replace your forks, leave the front wheel alone and if you need more rubber in the rear, get a set of Dunlop K591's for grip and higher speed rating. Outside of that, you'll be spending way too much money just to get a little more handling, and even after all this you still have the weight of the bike to deal with.
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Actually the solution is simpler than longer forks (which would look a little odd IMO) Put longer shocks on the back. This contributes to the desired goal anyway, as it also pulls in the rake angle a little. Doing these mods can greatly enhance the handling of the bike.

http://members.cox.net/88inchsporty/DSC_0125%20cropped%20and%20fixed.JPG