Belt Tensioner Roller RPM vs Ground Speed

[Snowbelt Spyder]

Just thought I would put this out there in a new post rather than tack onto the other one. Lately we have seen some reports about vibration dampener roller failures and possible replacements for Doc’s roller. There has been some replacement rollers suggested, and fortunately the spec sheets are available, which show that the maximum rated roller speed is 8000 RPM. Sounds high, but I started to wonder just what that means in real life operation of the Spyder. Others have as well. Turns out, I don’t think it’s high enough.

So, with nothing better to do today, I set out with my calculator and measuring tools in order to equate roller RPM to ground speed. We’ll work with English units, ( you folks across the pond can convert it ) and all of the measurements were taken from my machine - a 998 RT with the ribbed belt.

The roller being suggested has a diameter of 1.57”. That gives us a roller circumference of 4.9”. Next, we need to find out how many revolutions of the roller occur for one revolution of the drive belt. By direct measurement, my drive belt’s circumference is 112”. Thus, for each one revolution of the drive belt, the roller makes 22.9 revolutions. In that same single revolution of the drive belt, the Spyder moves forward 15.25’ (give or take a tenth) So, we now know that the roller makes 22.9 revolutions every 15.25 feet of bike travel.

So, how many revolutions does the roller make in a mile? We can set up our ratio now. In one mile, the drive belt makes 346.2 revolutions, and the roller makes 7928 revolutions. And of course, if we ride that mile in a minute - which is a speed of 60 MPH, then the roller is spinning at 7,928 RPM. Only a smidge below the 8000 maximum. In other words, that roller essentially reaches its maximum rated RPM when traveling at 60 MPH.

I don’t personally know what the rated RPM is on the bearings that Doc uses, or those that Lamonster uses. Both of these rollers have been seen to fail catastrophically. Doc’s roller is even smaller in diameter, closer to 1.25” - which will make it spin even faster. If his bearings are rated at the same 8000 RPM, then the ground speed to reach that number is even lower.

Looking at a hypothetical 2” roller, and doing all of the same math, it will be spinning at a rate of 6162 RPM at 60 MPH. If it has the same 8000 RPM bearings, that max will be reached at 77.9 MPH.

Bottom line is that a replacement roller for Docs arm, doesn’t only have to fit properly or have two bearings instead of one. It also has to have bearings with a sufficient RPM rating to handle the required vehicle speeds. That’s what we should be looking for. In the case of the rollers suggested, and perhaps Doc’s original one, they do not. I was surprised. Explains a lot. Feel free to double check my math or do your own.

 

[Lew L]

I'm sure your math is good. I'll be looking for a larger roller but the max RPM will be hard to find. While on vacation in Wyoming, I did 75 to 80 mph just to keep up with the regular traffic on the freeways and even secondary roads. And ,yes, fuel milage did drop off by 20% or so.

Lew L

 

[T.P.]

I'm reaching out to a supplier of high speed bearings, Because we need them to go way past 8000rpm's

Will see what I can come up with.

T.P.

 

[PMK]

Super informative and detailed write up.

For comparison, if the roller is spinning at over 100% max rated speed, while at just over 60mph, there is no way your engine would last at max rpm for long term continuous use either.

If anyone should be concerned, it might be the engineering team at BRP that devised the oem version.

 

[Cruzr Joe]

Very good info. :bowdown::bowdown:

 

[Peacekeeper6]

Sounds like you have to replace the roller every 10k miles or so as preventative maintenance, no ??

 

[BajaRon]

Much as I suspected. RPM issues may be the true culprit here.

Just too many failures on some otherwise well engineered products. You have to take into consideration that there is going to be some headroom on the manufacturer's 'Max RPM' bearing set. But continuously running these rollers at, near, or quite likely above Max RPM is certain to blow them up long before otherwise expected. I have not looked at how much clearance there might be for a larger roller. But the easiest, cheapest and quickest way to fix this IS with a larger roller.

I put together these 2 charts. I know no one ever goes 90 mph on their Spyder. Certainly, Not I!!! But I threw that in there just in case someone were to accidentally go that fast.

The chart on the left is running a stock size tire. The one on the right is running the popular, and slightly larger diameter, 215/60/15 tire. That helps a little for those of you running this tire. But probably not worth buying a new tire just to get your dampener pulley RPM's down.

So, looking at these numbers I think we may be asking the wrong question. It's not so much WHY these rollers are failing. But how is it that they aren't failing sooner at these speeds?

 

[ChicagoSpyder]

The bearing in the Lamonster wheel is a 6202 RS, which should be good for 12,000 RPM.
https://www.micropoly.com/technical-information/maximum-rpm-calculator.html

So I've read about catastrophic failure when the bearing detonates, I'm assuming this takes out the belt. Since I'm fairly new to the Spyder world what can I expect when the drive belt grenades on one of these machines?

Also since we're talking about bearings, who manufactures the bearing and to what spec has much to do with bearing load and life, come to think of it I don't recall seeing any manu name on the bearing that came with my Lamonster tensioner, which just came in the mail the other day, and I haven't installed yet.

 

[Peacekeeper6]

Guess that’s why I’m not in such a hurry installing a belt tensioner.

1) The bearings are spinning at such a rapid rate that catastrophic failure is imminent, and

2) I don’t usually go faster than 65 mph and have that dreaded drive belt vibration.

 

[PMK]

Not sure where 8000 rpm was found as max revs.

Just did a simple search and the SKF brand bearing had a reference rpm of 43,000 rpm and a limiting rpm of 28,000 rpm.

The 8000 rpm seemed very low to me. When I raced model cars, we were turning in excess of 40,000 rpm constantly on slightly smaller bearings.

 

[Gwolf]

Not sure where 8000 rpm was found as max revs.

Just did a simple search and the SKF brand bearing had a reference rpm of 43,000 rpm and a limiting rpm of 28,000 rpm.

The 8000 rpm seemed very low to me. When I raced model cars, we were turning in excess of 40,000 rpm constantly on slightly smaller bearings.

Model cars are not run for hours at the time without a cooling down period. It would be something like the duty cycle figured in.

 

[PMK]

Model cars are not run for hours at the time without a cooling down period. It would be something like the duty cycle figured in.

Well sort of duty cycle, but not really. Exceeding maximum rpm is exceeding the max rpm, regardless of duty cycle.

As I stated, the 8000 rpm seemed very low after some time from thinking about it since my first post. Even the least expensive bearings had rpm ratings over 8000 rpm.

We did not install a belt damper / tensioner device on our Spyder for the very reason knowing these rollers would have the dickens spun out of them. Kind of a keep it simple approach.

My experience with high rpm ball bearings used in various installations would also have me look into whether or not the actual roller bore steps are precise in relation to the width of the crush spacer.

In the case of Docs, he did not use crush spacers and had counted on correctly tightening the bearing preload nut. Not good or proper in my opinion.

If the plastic rollers expand with heat, this situation can add tremendous preload into the bearings causing premature failures. The correct design would employ one of the various type spring washers on the bearing side of the roller and adequate clearances to keep bearing preloads minimal.

This would also require a mounting stud that is double ended, and secures to the arm with a nut, and the opposite end is a nut to secure the bearings.

If a thru bolt design is to be retained, the crush sleeve is mandatory between two bearings while the plastic pulley must accommodate not adding preload. This may be the reasoning behind BRP using a single bearing. That design overcomes differences in expansion and has no concern in regards to bearing preload, but does surrender support of the roller.

A more expensive double row bearing could also eliminate preload concerns while offering best support of the roller.

Still though, if 8000 rpm is truly max rated revs, nothing will survive.

 

[BajaRon]

The bearing in the Lamonster wheel is a 6202 RS, which should be good for 12,000 RPM.
https://www.micropoly.com/technical-information/maximum-rpm-calculator.html

So I've read about catastrophic failure when the bearing detonates, I'm assuming this takes out the belt. Since I'm fairly new to the Spyder world what can I expect when the drive belt grenades on one of these machines?

Also since we're talking about bearings, who manufactures the bearing and to what spec has much to do with bearing load and life, come to think of it I don't recall seeing any manu name on the bearing that came with my Lamonster tensioner, which just came in the mail the other day, and I haven't installed yet.

Usually, when one of these vibration dampeners fails, it shreds the belt. It has to be replaced, but it will usually get you home.

Not sure where 8000 rpm was found as max revs.

Just did a simple search and the SKF brand bearing had a reference rpm of 43,000 rpm and a limiting rpm of 28,000 rpm.

The 8000 rpm seemed very low to me. When I raced model cars, we were turning in excess of 40,000 rpm constantly on slightly smaller bearings.

The specs. are listed in the description for this roller.

Model cars are not run for hours at the time without a cooling down period. It would be something like the duty cycle figured in.

I used to run slot cars back in the day. Even back then the RPM's were pretty outrageous. But those bearings don't really carry much load. It is a combination of factors including load, temperature, duration and RPM. Any one of which, or in combination can create a situation that causes a bearing to fail.

 

[PMK]

Usually, when one of these vibration dampeners fails, it shreds the belt. It has to be replaced, but it will usually get you home.



The specs. are listed in the description for this roller.



I used to run slot cars back in the day. Even back then the RPM's were pretty outrageous. But those bearings don't really carry much load. It is a combination of factors including load, temperature, duration and RPM. Any one of which, or in combination can create a situation that causes a bearing to fail.

Are you referring to the white colored roller?
Someone posted the use of 6202-2rs bearings. Those are higher rom rated than 8000 rpm.

 

[Peter Aawen]

This thread:

https://www.spyderlovers.com/forums...er-upgrade-for-Doc-Humphries-Vibration-Damper

And in the thread, post #13 shows a spec sheet displaying the max rpm for the alternative roller that started all of this recent 'roller' discussion off... :thumbup:

 

[PMK]

This thread:

https://www.spyderlovers.com/forums...er-upgrade-for-Doc-Humphries-Vibration-Damper

And in the thread, post #13 shows a spec sheet displaying the max rpm for the alternative roller that started all of this recent 'roller' discussion off... :thumbup:

Seems an odd way to group other brands within the 8000 max rpm range. If we know that Lamonster uses a 6202-2rs set of bearings, those bearings are well above the 8000 rpm limit of this replacement roller. So in fairness, those buying and installing the replacement roller you mentioned in the linked topic / post #13 is an inferior roller for this application.

Possibly the best setup is not to even have a plastic roller. Simply stack an appropriate number of bearings, each with a thin shim between them to prevent any binding preload and let the belt roll on the bearings outer races. No plastic to fail, no dissimilar rates of expansion causing induced preloads that can destroy the bearings, lower cost and simpler replacement.

So in short, that White referenced roller is a no go and ensure you have a quality replacement, and likely replace the bearings as a scheduled maintenance task that align with other maintenance tasks.

 

[BajaRon]

Are you referring to the white colored roller?
Someone posted the use of 6202-2rs bearings. Those are higher rom rated than 8000 rpm.

Yes, the link to the recommended roller stated a Max RPM of 8,000 RPM. It appears that the Lamonster Garage replacement roller has a 12,000 Max RPM.

 

[RICZ]

To make sealed bearing last longer, remove the seal - it's just pressed in lightly - and add more grease to the paltry amount that's in there.

 

[Papa103]

This explains why BRP doesn't put them on from the factory. The problem from a grenaded tensioner might be worse than a little belt vibration.

 

[PMK]

Yes, the link to the recommended roller stated a Max RPM of 8,000 RPM. It appears that the Lamonster Garage replacement roller has a 12,000 Max RPM.

Based off the original post here, and comments on how the Lamonster setup uses a larger roller, seems the Lamonster setup is over 100 mph to reach the max rpm rating of the roller.