Bigger tires = Less power?

[cubfan1968]

The standard rear tire for a Six Day is 3.50 x 18. My question is how much power is lost when a bigger tire is used like a 4.00 or 4.60?  [?][?]

Rod Whitman
Omaha, Nebraska
1972 Six Day (Rider)
1972 Six Day (Project)

[Tony Price]

The modern 400 series tires like Kenda or Cheng Shin are about the same size as the old 3.50 tires.

Tony

[Doug Wilford]

The 400:18 was the tire of choice on all CMF models 72 +  clearance through the swing arm was more of a factor than the power loss.  If you don't have traction, what difference does HP mean.  Sprockets can be changed to keep you on the pipe.
Have Fun!

[conrad2]

Rod, I jsut put a 4.00 x18 trie on my Six Days and it may have lost a little power(very little) but the extra traction is well worth it. Like Doug says HP doesn't matter if the bike won't hook up.
All of the "experts" on Six Days told me to run a 4.00,I make sure to listen to them!! It might rub the chain gaurd a bit but it works.
Plus it makes the bike look badder!
Conrad

Conrad Pfeifer
1972 Penton Six Days

[Paul Danik]

I put a 4.00 X 18 on my bike just before the ISDTRR, the tire I took off was a 4.50 X 18.  I used to always run 4.50 X 18 in the really muddy slop, it takes a little bit to get it to turn freely but it really pays off in ugly conditions.  It is best to have your carb adjusted properly if you plan to lug around a 125cc machine with a 450 X 18 on it in the muck, if you are rich at the bottom it might make for a long day.
Paul

[Speedy]

quote:Originally posted by cubfan1968

The standard rear tire for a Six Day is 3.50 x 18. My question is how much power is lost when a bigger tire is used like a 4.00 or 4.60?  [?][?]

Rod Whitman
Omaha, Nebraska
1972 Six Day (Rider)
1972 Six Day (Project)

Oversized tires dont bring anything.
I use a 410 on my 250 + 350

Helmut Clasen KTM
162 Hillcrest Ave
L9H 4Y3
Dundas Ontario Canada
Ph.905-627-5349
[email protected]
http://speedy_c.tripod.com
Sachs MC-GS 250-7A reeds
Hercules 350-7A 77
Hercules 250-7A 76
Hercules 250 GS 7A 77
Zuendapp 125 GS
KTM 200 EXC 2003
KTM DUKE 96 Spec.

[Paul Danik]

Ah Speedy, the soils are different in Mars:)  I hope you were able to get your travel trailer back after the ISDTRR.
Paul

[wfopete]

For what it's worth; I have used a Michelin trials tire in every AHRMA cross country event I competed in (7 or this year except Barber and the ISDTRR. I have had zero traction issues with the trials tire.  At the Qualifier Warm Ups in Arkansas there were times where the trials tire gave me too much traction as I needed to climb up on the tank or cut the throttle to keep from looping out while climbing a first gear hill covered with roots and rocks. The trials tires cost more but wears great. I also use them on my KTM 300X/C-W when racing Hare Scrambles here in Arkansas. While others go through 2,3 or 4 tires in a season, I still have life on the trials tire.

With that said, I tossed the 'Piner's chain guard (for tire clearance) and put on a new Michelin S12 for the Barber and ISDTRR events.  I theorized that I would rather give up a pinch of power to pull the bigger tire than get stuck because of lack of traction. Plus you get addional rim protection with the wider tire. I'm glad I switched for those two races, especially the ISDTRR, where no matter how deep the mud, ruts or sand that S12 pulled me through with no problem.  I probably don't think I could have said that with the trials tires!

BTW, Dirt Rider magazine just gave trials tires the runner up spot for product of the year.  Try it you'll like it.

Pete Petrick  


'01 KTM EXC 520, '74 YZ 250, '86 Honda XR 250, '71 Hodaka 100, '74 SUZUKI TM 400, '73 Penton Jackpiner

[bentrims]

My current 6 days race bike has had the same modern 100/90-19...yes 19" Excel rim. Has never failed pulling holeshots in 125 classic class.

I put a veneer on it and it reads 4.70 outside. Keep that compression around 150-155 psi and she will pull it easy.

We always ran 4.50 tires on our 125s to float through the deep sand of a Florida winter series with great success.
Tom Benolkin

[Dwight Rudder]

quote:Originally posted by wfopete

For what it's worth; I have used a Michelin trials tire in every AHRMA cross country event I competed in (7 or this year except Barber and the ISDTRR. I have had zero traction issues with the trials tire.  At the Qualifier Warm Ups in Arkansas there were times where the trials tire gave me too much traction as I needed to climb up on the tank or cut the throttle to keep from looping out while climbing a first gear hill covered with roots and rocks. The trials tires cost more but wears great. I also use them on my KTM 300X/C-W when racing Hare Scrambles here in Arkansas. While others go through 2,3 or 4 tires in a season, I still have life on the trials tire.

With that said, I tossed the 'Piner's chain guard (for tire clearance) and put on a new Michelin S12 for the Barber and ISDTRR events.  I theorized that I would rather give up a pinch of power to pull the bigger tire than get stuck because of lack of traction. Plus you get addional rim protection with the wider tire. I'm glad I switched for those two races, especially the ISDTRR, where no matter how deep the mud, ruts or sand that S12 pulled me through with no problem.  I probably don't think I could have said that with the trials tires!

BTW, Dirt Rider magazine just gave trials tires the runner up spot for product of the year.  Try it you'll like it.

Pete Petrick  


'01 KTM EXC 520, '74 YZ 250, '86 Honda XR 250, '71 Hodaka 100, '74 SUZUKI TM 400, '73 Penton Jackpiner

I tried 2 Dunlop trials tires.  Destroyed both in 65 miles.  Good traction on hard pack , rocks and roots.  Mud is marginal. Suprising good traction on sand.  Braking is HORRIBLE.  I tried to slide through every fast turn.  I went back to Pirelli MT16 tires.  OH, By the way I use the Cheng Shin C183A on all my small bore bikes. I use the 350X18 on my Hodaka and do not lack for traction.  A 410X18 is similar in width to a 350 but with a lower profile. If you are putting a 400X18 on your Six Day 125, I suggest the C183A. It is a Barum copy and isn't quite as aggressive as a C755 Cheng Shin and lasts longer. Really hooks up in the rocks and roots.  If you have a Jackpiner I highly suggest a 110/100X18 ( 400X18 ) Pirelli MT16.  It uses a older tread pattern and although it resembles a Metzler MX Enduro or a Pirelli MT08, it is made with a modern carcass and rubber compound.  I use them ( 120/100X18, 450X18 ) on my 525EXC KTM. A modern tire like a Michelin S12 has no place on a vintage bike.  Too much traction.  Modern tread designs look wrong on a vintage bike. Michelins didn't even make knobbies till about 1986.
IMHO,
Dwight

Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.

[Dwight Rudder]

quote:Originally posted by bentrims

My current 6 days race bike has had the same modern 100/90-19...yes 19" Excel rim. Has never failed pulling holeshots in 125 classic class.

I put a veneer on it and it reads 4.70 outside. Keep that compression around 150-155 psi and she will pull it easy.

We always ran 4.50 tires on our 125s to float through the deep sand of a Florida winter series with great success.
Tom Benolkin

First of all a 19" rim is wrong on a vintage bike made in the 70's.  I seriously doubt also that the tire would stay on the rim with 150 PSI!
Also a 450 Metzler MX Enduro was about the same size as the 400 Pirelli MT16.  The 450 Multicross was a HUGE tire meant only for open class bikes.  A 18" tire is better to prevent flats as you have more sidewall cushion.  A 19" rim is marginally better on a hard pack blue groove track like in SoCal. Or a SX track.
IMHO,
Dwight

Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.

[wfopete]

quote:Originally posted by Dwight Rudder

quote:Originally posted by bentrims

My current 6 days race bike has had the same modern 100/90-19...yes 19" Excel rim. Has never failed pulling holeshots in 125 classic class.

 Keep that compression around 150-155 psi and she will pull it easy.

We always ran 4.50 tires on our 125s to float through the deep sand of a Florida winter series with great success.
Tom Benolkin

  I seriously doubt also that the tire would stay on the rim with 150 PSI!

Dwight,

I think (hope) Tom was talking about the compression in his motor.  You destroyed 2 trials tires in 65 miles? What the hell were they on, your 525?  Don’t tell me you did it on your Hodaka! I have not used a Dunlop trials tire, so I can't speak for it's durability.

Pete Petrick

[TGTech]

Rod,

   I see that everybody is giving you their take on what size of tires to use, but I don't see anybody answering your question. I don't know I can give you an accurate answer, but I can let you know the actual effect of different size tires.

   First off, when you go to a larger tire, you have to take in effect the diameter of the tire as well as the width. A wider tire with a lower cross section, can end up with the same effect, depending on the actual dimensions.

   During the steel tank/cast iron cylinder days, the 125s used a 3.50 rear tire, but when the aluminum cylinders and eventually the CMF frames came around the horsepower levels of the bike rose, and they would work well with the 4.00 tires.

   Another issue that must be taken in account, is the bike's gearing.  The effect of a larger rear tire, can be countered by adding a couple of teeth to the rear sprocket. By going this direction, you can retain the acceleration rate, but of course, you'll lose a little top speed.

   When Metzler came out with the 4.10 rear tire, we pretty much went to that tire, because it had the footprint that we wanted, but because it was a little lower in aspect than the 4.00. Later on the metric type measurements came out, they began to make even lower profile tires with wider foot prints, which gave us even more options.

   As for the actual horsepower loss, that actually isn't going to happen, because you aren't actually affecting the engine. But larger tires, width or diameter, will affect the bike's acceleration. By changing the gearing, you can adjust that effect.

   Personally, I liked the low profile tires with a wider footprint, providing it clears the chainguard and swing arm. One thing you have to keep in mind regarding the low profile tires, is that they don't protect the rims as well when you're riding in rocks.

   I hope this information helps you out a little.

Dane

[tlanders]

Dane,

Don't you mean subtracting a few teeth? "The effect of a larger rear tire, can be countered by adding a couple of teeth to the rear sprocket. By going this direction, you can retain the acceleration rate, but of course, you'll lose a little top speed."

Teddy

[TGTech]

No, Teddy. When you add teeth, you lower the gear ratio (higher number/lower ratio) and retain the acceleration rate. The larger tire, is harder for the engine to turn, so by adding teeth to the rear sprocket, you counter that effect.

Dane