Theoretical top speed

[Dmagg]

I know the 2019 exr is electrically limited to 76mph. Anyone know what the theoretical top speed is? This thing still pulls pretty hard until it hits its limiter. Wouldn’t surprise me if it’s 95 mph+

 

[datadog]

In a vacuum or on a treadmill?

It's an aerodynamic brick with a rider. I'm doubting the optimistic figure. Gearing could possibly get it there.

 

[Dmagg]

The zero fxs is “limited” to 85 mph and has a 32 kw engine compared to the exr’s 38+ kw engine.

 

[TCMB371]

Our bikes are not speed limited, they are motor RPM limited (14000 rpm). So, with gearing, the bikes can go faster at the expense of acceleration.

Aerodynamic drag is the ultimate killer here. Our very upright offroad bikes have terrible aerodynamics, meaning a lot of power is used (wasted) to push through the air. Aerodynamic drag is logarithmic, so if you double the speed, drag increases 4 fold. Also, the battery heats up and approaches thermal limits when under load for a long period of time.

Aerodynamic drag is defined as :
Cd*A = (Coefficient of Drag) * (Frontal Area).

So either improve the shape of the object (More streamlined to promote laminar flow) or reduce the frontal area. Better yet, try to do both. There probably is an equation out there that defines how much power is needed to push an object through the air - given its exterior shape, frontal area, rolling resistance of tires, etc

@ElectroBraap did a 13.3 @ 95.56mph on the @Mark911 built "Electrom", which has the Alta MX powerplant with 42hp and modified gearing. Keep in mind his frontal area would be a decent amount less than a regular Alta Redshift chassis.

I suspect 100mph is achievable on a MXR or EXR with modified gearing, rider in crouched position, and starting with a cold battery. Higher MPH if the bike is lowered and the bike+rider combo made more streamlined.

 

[Dmagg]

What a great answer. Thanks. Would gearing potentially increase the bikes range if a significant portion of the travel is at ~50mph compared to staying in the current config with a relatively high rpm at that speed?

 

[Redwolf]

Changing the gearing would not improve range in any meaningful way at that velocity, without doing something to dramatically improve aerodynamics.

 

[datadog]

There are simple answers, and there are more complicated ones.

 

[F451]

Test plan:
Stock Alta run up to top speed. Note top speed and local conditions (weather, wind, altitude, etc) for this run and all runs below.
Stock Alta at sustained top speed run until charge is depleted. Note mileage.
Taller gearing run to top speed. Any change?
Taller gearing sustained top speed run until charge is depleted. Note mileage, any change?
Stock Alta with clip ons and TZ250 or similar full body work run up to top speed. (or w/supermoto style wheels/tires)
Stock Alta with clip ons and TZ250 or similar full body work sustained top speed run until charge is depleted. (or w/supermoto style wheels/tires)

Would be a fun exercise.

Anyone taken their Alta to Bonneville yet?

From a last minute 300 mile left turn on the way home from Vegas back in 2011:

 

[leeo45]

Test plan:
Stock Alta run up to top speed. Note top speed and local conditions (weather, wind, altitude, etc) for this run and all runs below.
Stock Alta at sustained top speed run until charge is depleted. Note mileage.
Taller gearing run to top speed. Any change?
Taller gearing sustained top speed run until charge is depleted. Note mileage, any change?
Stock Alta with clip ons and TZ250 or similar full body work run up to top speed. (or w/supermoto style wheels/tires)
Stock Alta with clip ons and TZ250 or similar full body work sustained top speed run until charge is depleted. (or w/supermoto style wheels/tires)

Would be a fun exercise.

Anyone taken their Alta to Bonneville yet?

Interesting. Let's see .....

I have a stock ALTA "R" (two in fact).
I have relatively smooth DOT tires that fit the stock wheels.
I have sprockets and spare wheels to change the gear ratios.
I have a roadracing fairing, clip ons, and 17" wheels & tires that will fit an ALTA.

However, two remaining problems for the test plan ....

I don't have a place for a sustained high speed test without danger to myself, others, and my wallet.
I am 6'-3" tall and I am known as 'the moving billboard' in bicycle pacelines.

I suppose someone else will need to pull this off.

 

[Silent But Dirty]

Here is the records that were set on a MX in 2017.

 

[F451]

Interesting. Let's see .....

I have a stock ALTA "R" (two in fact).
I have relatively smooth DOT tires that fit the stock wheels.
I have sprockets and spare wheels to change the gear ratios.
I have a roadracing fairing, clip ons, and 17" wheels & tires that will fit an ALTA.

However, two remaining problems for the test plan ....

I don't have a place for a sustained high speed test without danger to myself, others, and my wallet.
I am 6'-3" tall and I am known as 'the moving billboard' in bicycle pacelines.

I suppose someone else will need to pull this off.

Well, I'm nominating you for the moment. Please drop everything in your life and get on this and report back to us. Thanks. Lol.

No seriously, this would be fun. I wish I was healthier, would get my butt down to Bonneville next year for some fun. -Eddie

 

[F451]

Here is the records that were set on a MX in 2017.

View attachment 4084

Wow. Fantastic results. Anymore details posted anywhere? Thanks for sharing. -Eddie

 

[Silent But Dirty]

Wow. Fantastic results. Anymore details posted anywhere? Thanks for sharing. -Eddie

As far as I know, these were done on the demo bike that Skagit Powersports had. The M class is stock, and I think the other class they added a fairing. Not sure about what gearing they ran.

 

[TCMB371]

I made a quick theoretical speed calculator for our bikes. Just input the tire diameter (inches) and the mph for each sprocket combination will be computed.

Alta Redshift Sprocket Calculator

 

[Judaslefourbe]

Remember that tires expand at speed too.

 

[TCMB371]

Remember that tires expand at speed too.

Not even going to attempt to work out the gnarly equation for tire expansion

 

[Judaslefourbe]

If memory serves, for the Enduro tires, it was 1 inch at full speed, for reference.

 

[Fog 25]

I made a quick theoretical speed calculator for our bikes. Just input the tire diameter (inches) and the mph for each sprocket combination will be computed.

Alta Redshift Sprocket Calculator

View attachment 4093[/MXR Top Speed Test
Your chart is real close

 

[Fog 25]

I was thinking of doing a top speed test in each map next.

MXR Top Speed Test

 

[Caryder]

I already did “a the test”. While I did use a sprocket calculator to figure out what combo I could use to keep the chain length the same, it verified 15/48 would work relative to 13/53 stock sprockets. I have 18” rim streetish biased tire (Shinko 705). About the same height as my worn knobby. Then I just went out and rode it. I didn’t have a good area to do a top speed run (only a half mile, but with a running start). GPS said 90mph but it didn’t feel like I had enough room and I wasn’t at full tuck (but I’m only 5’6” ) my sprocket calculator implied 96 mph at top rpm.