xr80 sprocket help

[jdunlap68]

Hey all, I have a 1991 xr80 flat tracker that is geared to low. What can I expect if I change the front sprocket to a 16T, it has a 14/49 on it now, and I need more topend.

Thanks

Jay

[ACDNate]

Going 2 up on the front is a pretty big jump. Gearing Commander doesn't have the stock ratio's for the xr80 to use as a calculator.

If you make that big of a jump be sure and test it before you get to the track. I made a similar jump only to find out that I could no longer pull 5th gear. That certainly didn't help my lap times...

[theraymondguy]

Assuming stock clutch and rear tire, about 5-6mph difference wrung out in 5th.

I believe stock gearing is 14/46, so currently you are setup for shorter than stock gearing.

Going back to stock gearing would represent about 2-3 mph gain over current, wrung out in 5th.

I would say use the largest front sprocket possible, matched to the largest rear possible, a 15 tooth front sprocket would be the closest choice with your 49 rear.

W.r.t. ACDNate's post; if you haven't added power to the engine, you honestly shouldn't expect to add gearing without sacrifice.

http://honda50.com/speedcalc/speedcalculator.html

This speed calculator is handy, however it assumes no losses (surface etc.).

Edited January 5, 2012 by theraymondguy

[jdunlap68]

Thanks, I'll look into 15t. I'm also looking at Powell 95cc big bore & a hot cam. I'm running with some xr100's, so gonna see if that helps without getting into the bottom end. Any thoughts? Thanks again.

[jdunlap68]

Powroll sorry, geez!!! Lol

[socalxr]

IMHO if you go to a 16t on and 80, it will be so slow out of the gate you will be trying to play catch up the whole race. The 80 is just a plain slow bike. Fun, but slow. How long is the track?

[jdunlap68]

The track is just less than 1/4mile, clay, banked oval. The class I run in can't be higher than 125cc, so I'm willing to put a little into the 80 if it will be competitive. If not, than thinking I should just get a xr100 or ttr125. I just don't have some of that topend needed at the end of the straights.

Thanks

Jay

[ACDNate]

For less money you should be able to find a 100 and be ahead of the curve. Then a 120kit is relatively inexpensive. Just my 2cents though...

[theraymondguy]

For less money you should be able to find a 100 and be ahead of the curve. Then a 120kit is relatively inexpensive. Just my 2cents though...

I'd like to see how a XR 80/95cc stacks up against the XR100/120bbk;

The 80 is 10lbs lighter, has a close ratio trans by comparison to the 100, lighter crank ass'y, lower ride height/center of gravity and lower unsprung weight. No real cost difference between the two kits (powroll 95cc vs. BBR 120) once machining costs are accumulated, a touch more compression though it does give up displacement. The BBR cam adds no performance value, so that cost is fixed as well...

Gad, need to ride more and bench race less. Winter sucks.

[socalxr]

Years ago I had a 95cc kit. It's an ok match for stock 100, but not even close to a decently built 120. To make the 80 comparable, it needs to a 121cc, which is a stroked 95cc.

[jdunlap68]

Thx guys, good info, now to figure out which way to go. I do think if I can add a little more power to the 80, that I will have some advantage. There is a big difference in the ride heights, it has a nice sweet spot, up on the bars, tail hanging out there, boy I do hate winter!!!

God bless

Jay